Hybrid Capsules via Self-Assembly of Thermoresponsive and Interfacially Active Bionanoparticle-Polymer Conjugates

New bionanoparticles have been prepared from horse spleen ferritin by grafting thermoresponsive poly(N-isopropyl acrylamide) (PNIPAAm) and photo-crosslinkable 2-(dimethyl maleinimido)-N-ethyl-acrylamide (DMIAAm) from the protein surface. The 72 addressable amino groups on the exterior of HSF were modified with N-hydroxysuccinimide-activated 2-bromo-isobutyrate to form a macro-initiator for atom transfer radical polymerization, which was performed in water/DMF solutions at low temperature. The modifi cation of the HSF and the presence of the polymer shell were confirmed by size exclusion chromatography (SEC), sodium dodecyl sulfate-polyacrylamide gel-electrophoresis, transmission electron microscopy, and scanning force microscopy. The thermoresponsive behavior of the ferritin-PNIPAAm conjugates was investigated in solution by UV-vis spectroscopy showing a phase transition in the form of a cloud point around 32 degrees C. Further, dynamic light scattering revealed an increasing hydrodynamic radius around this transition, indicating aggregation of the particles at elevated temperatures which was confirmed by transmission electron microscopy. Initial experiments show that the particles are highly surface active, much more than the individual components alone, which was demonstrated by pendant-drop interfacial tension measurements. This leads to the fact that they form stable Pickering emulsions, i.e., emulsion droplets decorated with polymer-modified bionanoparticles which can be cross-linked successively. This allows the formation of capsules with thermoresponsiveness for controlled release purposes, e.g., in drug delivery.